The present invention relates to a Waveguide Grating Router (WGR) and, more particularly, to a WGR having a large number N of input and output ports.
Large Nxc3x97N waveguide grating routers (WGR) represent an excellent solution for providing large optical cross-connects: They are fully passive elements and they can provide strictly non-blocking connections for a set of N optical channels. [1-5]. (Note in this specification, a reference to another document is designated by a number in brackets to identify its location in a list of references found in the Appendix)
However, due to the intrinsic diffraction characteristics of the grating, restrictions limit the size of a Nxc3x97N WGR. Additional and even more severe limitations arise if the WGR is designed to cross-connect channels which are equally spaced in frequency [4,6] as opposed to being equally spaced in wavelength.
Because the number of wavelengths being used in an optical system is constantly increasing, there is a continuing need to increase the size of the Nxc3x97N WGRs used as optical cross-connects.
In accordance with the present invention, we have recognized that because of the intrinsic diffraction characteristics of the grating, restrictions in the size of N generally happens when N approaches the diffraction order m at which the grating operates. We have developed a technique for maximizing N in a Nxc3x97N WGR device for channels equally spaced either in frequency or in wavelength. For the wavelength case, N is increased by appropriate changes in the spacing of the output ports of the WGR and/or by slightly correcting the channels wavelengths.
More particularly, the N in a Nxc3x97N WGR is maximized for input signals including N equally spaced wavelengths by using an output coupler having N output ports that are shifted from their original uniformly spaced position. In another embodiment used with input signals having N wavelengths or frequencies, the N in a Nxc3x97N WGR is maximized by using N wavelengths or frequencies that are not equally spaced. In yet another embodiment, used with input signals having N wavelengths or frequencies, the N in a Nxc3x97N WGR is maximized by using an output coupler having N output ports that are spaced to maximize the weakest signal transmission coefficient of at least one of the N wavelengths or frequencies from any of the N input ports.